a) Field of the Invention
The invention relates to a locking device of a steering column adjustable in at least one adjustment direction, with at least one locking part, associated with the adjustment direction or one of the adjustment directions, which comprises at least one first and at least one second toothing, and at least one counterlocking part associated with this adjustment direction, which comprises at least one first and at least one second countertoothing, and with an openable and closable tensioning arrangement, in the open state of which the first and second toothings are spaced apart from the first and second countertoothings and in the closed state of which the teeth of the toothings of the locking part and of the counterlocking part engage one another, and the teeth of the toothings and of the countertoothings extend transversely to this adjustment direction and successive teeth of the toothings and of the countertoothings are each spaced apart equidistantly from one another and the tips of the teeth of the toothing and of the countertoothings are each disposed in planes.
b) Description of Related Prior Art
Adjustable steering columns are known in various implementations. Conventionally the length of the steering column as well as also its inclination or height can be changed in the open state of the locking device. To arrest the shell tube receiving the steering spindle in the closed state of the locking device, for example, packets of plates crossing one another can be provided, of which the one is secured in place on the shell tube and the other on a console part stationary on the chassis, and through which penetrates a tensioning bolt and which are mutually deadlocked by means of the tensioning arrangement. Such an adjustable steering column is disclosed for example in EP 0 802 104 B1. To permit the adjustment, in the plate packets as well as in the shell tube and in the console part intersecting elongated holes are disposed through which penetrates the tensioning bolt. One of the disadvantages in steering columns comprising locking devices with plates is that the attainable retaining forces in the closed state are restricted to friction and that for attaining as high as possible a retaining force in the closed state a relatively large number of plates is required, whereby in the open state of the locking device also a relatively high friction force must be overcome in order to adjust the steering column.
EP 0 836 981 B1 discloses further an adjustable steering column with a locking device of the type described in the introduction, in which toothed parts are provided, whose teeth engage one another in the closed state of the locking device. Adjustment of the steering column in the opened state is very smooth. However, in the case of such a locking device the problem may be encountered that the tips of the teeth of opposing toothings are directly oriented toward one another (tooth to tooth position) and strike one another when the tensioning arrangement is being closed, such that the locking device cannot be closed properly. In the event of a crash, this can lead to an uncontrolled shifting of the steering column. In addition, closing the tensioning arrangement in the event the tips of the teeth strike one another is not possible at all or incompletely or only by exerting a strongly increased force or only after a further adjustment of the steering column.
For that reason different devices have already been proposed, by means of which the striking of the tooth tips when closing the tensioning arrangement is to be prevented. For this purpose in the devices of DE 198 39 496 A1 and U.S. Pat. No. 5,787,759 A a swivellable bearing of one of the two parts comprising the tooth bars is provided. In the device of DE 39 14 608 C1 a latch element supported displaceably in the direction of the plane of the tooth engagement is provided, which furthermore is swivellable within limits about an axis parallel to the longitudinal extent of the teeth. From EP 0 796 780 A2 a guide pin is known, which is in contact on a lateral guide face on a structural part comprising the two tooth bars, and the guide pin has an inclination, which corresponds approximately to the flank inclination of the teeth. These devices are relatively elaborate in their constructions without the hazard of the tooth tips striking one another being excluded under all circumstances. On the two opposing tooth bars in the locking device of DE 198 46 292 magnets are provided and the free tips of the teeth oriented toward one another are repelled from one another by magnetic forces. In order to attain through these magnetic devices a shifting of the two structural parts in the case the tip of the teeth of the two tooth bars are in a position directly oriented toward one another, relatively high magnetic forces must be exerted, which entails considerable expenditures.